I believe in the 80% solution. Put your money to work rather than stuffing it in a mattress, but favor the 80%-of-optimal solution that's easy to set and forget, instead of the 100%-optimal solution that requires micromanagement, expertise, and luck.

To that end, keep only a little in savings (emergency fund), and put the rest in a 401k or IRA, invested in index funds. Index funds are a great 80% approach, because:

- They track an index (e.g. S&P 500) which is likely to go up and up in the long term

- They are very low cost since they are not actively managed

- You can watch them every day, or forget about them for two years

- Warren Buffet recommends them, and he seems to be doing okay